Telecommunications apparatus and methods

ABSTRACT

A wireless telecommunication system includes base stations for communicating with terminal devices. One or more base stations support a power boost operating mode in which a base station&#39;s available transmission power is concentrated in a subset of its available transmission resources to provide enhanced transmission powers as compared to transmission powers on these transmission resources when the base station is not operating in the power boost mode. A base station establishes an extent to which one or more base stations in the wireless telecommunications system support the power boost operating mode conveys an indication of this to a terminal device. The terminal device receives the indication and uses the corresponding information to control its acquisition of a base station of the wireless telecommunication system, for example by taking account of which base stations support power boosting and/or when power boosting is supported during a cell attach procedure.

This is a continuation of U.S. application Ser. No. 14/777,709 filedSep. 16, 2015, which is based on PCT/EP2014/057393 filed Apr. 11, 2014,which claims priority to British Patent Application 1306764.0 filed inthe UK IPO on Apr. 15, 2013 and European Patent Application 13190387.4filed in the European Patent Office on Oct. 25, 2013 the entire contentsof each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for use inwireless (mobile) telecommunications systems. In particular, embodimentsof the invention relate to methods and apparatus for providing coverageextension in wireless telecommunications systems.

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architecture are becoming able to support more sophisticated servicesthan simple voice and messaging services offered by previous generationsof mobile telecommunication systems. For example, with the improvedradio interface and enhanced data rates provided by LTE systems, a useris able to enjoy high data rate applications such as mobile videostreaming and mobile video conferencing that would previously only havebeen available via a fixed line data connection. The demand to deploythird and fourth generation networks is therefore strong and there is acorresponding desire to extend the coverage available in suchtelecommunications systems (i.e. there is a desire to provide morereliable access to wireless telecommunications systems for terminaldevices operating in coverage-limited locations).

A typical example of a coverage-limited terminal device might be aso-called machine type communication (MTC) device, such as a smart meterlocated in a customer's house and periodically transmitting informationback to a central MTC server relating to the customer's consumption of autility, such as gas, water, electricity and so on. Such a terminaldevice might operate in a coverage-limited location because, forexample, it may be located in a basement or other location withrelatively high penetration loss.

In some situations a terminal device in a coverage-limited situation ina particular communication cell served by a base station might be unableto receive communications from the base station unless specificprovision is made for it to do so. One simple way to increase coveragein this situation would be for the base station to increase the power ofits transmissions. However, a blanket increase in transmission powerfrom a base station would be expected to give rise to correspondinglyincreased interference in neighbouring communication cells. Analternative approach would be for the base station to in effectfocus/concentrate its available transmission power budget into a subsetof transmission resources (e.g. in terms of frequency) which areselected from within the base station's overall transmission resourcesand allocated for transmissions to coverage-limited terminal devices. Inthis manner increased power may be made available for communicating withterminal devices in “hard to reach” locations without exceeding a basestation's overall power budget. Such an approach may be referred to aspower boosting. Thus, a base station with power boosting capability mayfocus its available transmission power within a restricted subset oftransmission resources allocated to coverage-limited terminal devices.

This power boosting approach is schematically represented in FIGS. 1Aand 1B which show example plots of maximum allowed transmission power Pversus frequency f for two modes of operation for a base station in anLTE-based wireless telecommunication network. FIG. 1A represents anormal mode of operation in which the maximum allowed transmission poweris uniform across the base station's full operating bandwidth S_(BW)(e.g. 20 MHz) at a level of P₀. FIG. 1B, on the other hand, represents apower boosted mode of operation for the base station in which theoverall available transmission power is in effect concentrated withtransmissions being allowed at a power level P_(PB), which is greaterthan the power P₀ for the normal operating mode, across a bandwidthPB_(BW), which is less than the bandwidth S_(BW) for the normaloperating mode. It can be expected a base station will be adapted toswitch between normal and power boosted operating modes, for exampledepending on current or expected traffic conditions. The overalltransmission power will typically be broadly the same in both operatingmodes (i.e. the areas under the curves in FIGS. 1A and 1B will be thesame). For the sake of a concrete example, in one power boostedoperating mode implementation PB_(BW) may be approximately one quarterof S_(BW) (e.g. S_(BW)=20 MHz and PB_(BW)=5 MHz) while P_(PB) may beapproximately four times P₀. Thus, in this example implementation thebase station may transmit up to four times more power on transmissionresources allocated to a coverage-limited terminal device within thefrequency bandwidth P_(BW) without exceeding an overall power budget forthe base station. In practice, communications with specific terminaldevices on specific subcarriers may be made with less power than themaximum allowed, taking into account the conventional power controlmechanisms provided in wireless telecommunications systems.

Thus, a wireless telecommunications network adapted to provide coveragein challenging situations by power boosting may at times re-configureitself to concentrate its available transmit power into a number ofresource elements (REs) occupying in total less than the nominal systembandwidth. A coverage-limited terminal device may be allocated resourceson these power-boosted resource elements making it more likely to beable to use the cell.

As is well understood, in an LTE type network there are two RadioResource Control (RRC) modes for terminal devices, namely: (i) RRC idlemode (RRC_IDLE); and (ii) RRC connected mode (RRC CONNECTED). When aterminal device transmits data, RRC connected mode is required. In RRCidle mode, the core network (CN) part of the wireless telecommunicationssystem recognizes the terminal device is present within the network, butthe radio access network (RAN) part of the wireless telecommunicationssystem does not. As is conventional for an LTE-type wirelesstelecommunications network, a terminal device may conduct ReferenceSignal Received Power (RSRP)/Reference Signal Received Quality (RSRQ)measurements in communication cells in which it can operate and mayautonomously decide to camp on one particular cell (e.g. according toRSRP/RSRQ threshold tests and the Public Land Mobile Network (PLMN)identities of the cells) in order to receive system information (SI) andpaging messages. In accordance with this approach the base stationssupporting communications in the respective cells do not themselves playa role in cell selection for terminal devices in idle mode with theprocess of cell selection/reselection in idle mode being performedautonomously by the terminal devices. This is in contrast to thecell-change procedures in RRC connected mode in which case terminaldevices are under control of the RAN and the handover process is anetwork controlled behaviour (with assistance from terminal devicemeasurements).

A terminal device that could benefit from power boosting as describedabove to more reliably operate in a communication cell will typicallynot know at the point of trying to acquire or camp on a cell whether thebase station of the cell supports power-boosting. As a consequence, aterminal device may spend time and power resources undertaking a camp onprocedure for a cell, for example by decoding Primary SynchronisationSignalling (PSS), Secondary Synchronisation Signalling (SSS), a PhysicalBroadcast Channel (PBCH) and SI of a cell, and then subsequentlyundertake a random access procedure using Physical Random Access Channel(PRACH) resources to access the cell, only to find the cell does notsupport power boosting and so cannot reliably support communicationswith the terminal device on channels such as a Physical Downlink ControlChannel (PDCCH) and Physical Downlink Shared Channel (PDSCH).

Even for a base station which is able to support power boosting, it maybe that the above-discussed power boosting approach to extendingcoverage may not be supported by the base station at all times so as toreduce the impact on other terminal devices operating in the cell. Forexample, power boosting may only be supported at certain times of day ornight within a given communication cell according to when it is expectedthe resources required to properly support conventional terminal devicesoperating in the cell may be reduced. In these cases it may beappropriate for terminal devices requiring power boosting to wait(“sleep”) until such time that power boosting is supported beforeseeking to acquire the relevant cell.

There is therefore a need for schemes which assist in the process bywhich a terminal device which may benefit from power boosting forreliable communications in a wireless telecommunications system seeks tocamp on/access base stations of the wireless telecommunications system.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a methodof operating a terminal device in a wireless telecommunication systemcomprising one or more base stations which support a power boostoperating mode in which a base station's available transmission power isconcentrated to provide enhanced transmission powers in a subset of itsavailable transmission resources, the method comprising: receiving anindication of the extent to which one or more base stations support thepower boost operating mode in the wireless telecommunication system; andcontrolling acquisition of a base station of the wirelesstelecommunication system in a manner that takes account of the indicatedextent to which one or more base stations support the power boost mode.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modecomprises one or more indications selected from the group comprising:(i) an indication of whether or not one or more base stations areconfigured to have the ability to operate in the power boost operatingmode; (ii) an indication of times during which one or more base stationsare configured to use the boost operating mode; (iii) an indication ofavailable enhanced transmission powers for one or more base stationswhen operating in the power boost operating mode; (iv) an indication ofwhich downlink physical channels of the wireless telecommunicationssystem can be transmitted by one or more base stations using the powerboost operating mode.

In accordance with certain embodiments the step of controllingacquisition of a base station comprises choosing a base station toacquire from among a plurality of available base stations in a mannerthat takes account of the indicated extent to which one or more basestations support the power boost mode in the wireless telecommunicationsystem.

In accordance with certain embodiments the step of choosing a basestation to acquire is performed during a cell section or a cellreselection procedure of the terminal device.

In accordance with certain embodiments the step of controllingacquisition of a base station comprises delaying acquisition of the basestation for a period of time based on the indication of the extent towhich one or more base stations support the power boost operating modein the wireless telecommunication system.

In accordance with certain embodiments the method further comprises theterminal device entering a reduced activity mode during a period of timefor which acquisition of the base station is delayed.

In accordance with certain embodiments the method further comprisesderiving one or more characteristics of received signals from one ormore base stations in the wireless telecommunications system, andwherein the step of controlling acquisition of a base station also takesaccount of the one or more derived characteristics.

In accordance with certain embodiments the derived one or morecharacteristics are derived from reference signal received power (RSRP)measurements and/or reference signal received quality (RSRQ)measurements associated with reference signals transmitted by one ormore base stations in the wireless telecommunications system.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modein the wireless telecommunication system includes an indication which isspecific to an individual base station.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modein the wireless telecommunication system comprises an indication whichis applicable for a plurality of base stations.

In accordance with certain embodiments the step of receiving theindication of the extent to which one or more base stations support thepower boost operating mode comprises receiving from a first base stationan indication of the extent to which the first base station supports thepower boost operating mode.

In accordance with certain embodiments the step of receiving theindication of the extent to which one or more base stations support thepower boost operating mode further comprises receiving from a furtherbase station an indication of the extent to which the further basestation supports the power boost operating mode.

In accordance with certain embodiments the step of receiving theindication of the extent to which one or more base stations support thepower boost operating mode comprises receiving from a first base stationan indication of the extent to which a second, different, base stationsupports the power boost operating mode.

In accordance with certain embodiments the first base station is a basestation to which the terminal device is connected and the second basestation is a base station to which the terminal device is not connected.

In accordance with certain embodiments the step of controllingacquisition of a base station of the wireless telecommunication systemcomprises determining whether or not to disconnect from the first basestation and to connect to the second base station.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modeis received by the terminal device in communications received from oneor more base station to which terminal device is not connected.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modeis implicitly conveyed to the terminal device in association withtransmissions made by base stations in the wireless telecommunicationssystem for communicating other information.

In accordance with certain embodiments the step of receiving theindication of the extent to which one or more base stations support thepower boost operating mode in the wireless telecommunication systemcomprises receiving broadcast signalling from one or more base stationsand deriving the indication of the extent to which one or more basestations support the power boost operating mode from the transmissionresources used for the broadcast signalling.

In accordance with certain embodiments the broadcast signallingcomprises synchronisation signalling

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modeis received by the terminal device using explicit signalling.

In accordance with certain embodiments the explicit signalling comprisessystem information signalling received from a base station.

In accordance another aspect of the disclosure there is provided amethod of operating a terminal device in a wireless telecommunicationsystem comprising one or more base stations which support a virtualcarrier operating mode in which at least some downlink communicationsare made using a restricted subset of transmission resources selectedfrom within a system frequency bandwidth and comprising a restrictedbandwidth downlink channel having a channel bandwidth which is smallerthan the system frequency bandwidth, the method comprising: receiving anindication of the extent to which one or more base stations support thevirtual carrier operating mode in the wireless telecommunication system;and controlling acquisition of a base station of the wirelesstelecommunication system in a manner that takes account of the indicatedextent to which one or more base stations support the virtual carrieroperating mode.

In accordance with certain embodiments, the step of receiving theindication of the extent to which one or more base stations support thevirtual carrier operating mode comprises receiving from a first basestation an indication of the extent to which a second, different, basestation supports the virtual carrier operating mode.

In accordance with certain embodiments, the first base station is a basestation to which the terminal device is connected and the second basestation is a base station to which the terminal device is not connected.

In accordance with certain embodiments, the indication of the extent towhich one or more base stations support the virtual carrier operatingmode is received by the terminal device using explicit signalling.

In accordance with certain embodiments, the explicit signallingcomprises system information signalling received from a base station.

In accordance with another aspect of the invention there is provided aterminal device for use in a wireless telecommunication systemcomprising one or more base stations which support a power boostoperating mode in which a base station's available transmission power isconcentrated to provide enhanced transmission powers in a subset of itsavailable transmission resources, wherein the terminal device isconfigured to: receive an indication of the extent to which one or morebase stations support the power boost operating mode in the wirelesstelecommunication system; and control acquisition of a base station ofthe wireless telecommunication system in a manner that takes account ofthe indicated extent to which one or more base stations support thepower boost mode.

In accordance another aspect of the disclosure there is provided aterminal device for use in a wireless telecommunication systemcomprising one or more base stations which support a virtual carrieroperating mode in which at least some downlink communications are madeusing a restricted subset of transmission resources selected from withina system frequency bandwidth and comprising a restricted bandwidthdownlink channel having a channel bandwidth which is smaller than thesystem frequency bandwidth, wherein the terminal device is configured toreceive an indication of the extent to which one or more base stationssupport the virtual carrier operating mode in the wirelesstelecommunication system; and to control acquisition of a base stationof the wireless telecommunication system in a manner that takes accountof the indicated extent to which one or more base stations support thevirtual carrier operating mode.

In accordance with another aspect of the invention there is provided amethod of operating a base station in a wireless telecommunicationsystem comprising one or more base stations which support a power boostoperating mode in which a base station's available transmission power isconcentrated to provide enhanced transmission powers in a subset of itsavailable transmission resources, the method comprising: establishing anextent to which one or more base stations support the power boostoperating mode; and, conveying an indication of the extent to which oneor more base stations support the power boost operating mode to aterminal device operating in the wireless telecommunication system sothe terminal device can take account of the indication of the extent towhich one or more base stations support the power boost operating modefor controlling its acquisition of a base station of the wirelesstelecommunication system.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modecomprises one or more indications selected from the group comprising:(i) an indication of whether or not one or more base stations areconfigured to have the ability to operate in the power boost operatingmode; (ii) an indication of times during which one or more base stationsare configured to use the boost operating mode; (iii) an indication ofavailable enhanced transmission powers for one or more base stationswhen operating in the power boost operating mode; (iv) an indication ofwhich downlink physical channels of the wireless telecommunicationssystem can be transmitted by one or more base stations using the powerboost operating mode.

In accordance with certain embodiments the method further comprisestransmitting reference signals to allow the terminal device to deriveone or more characteristics of received reference signals for use inconjunction with the indication of the extent to which one or more basestations support the power boost operating mode when controllingacquisition of a base station of the wireless telecommunication system.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modein the wireless telecommunication system includes an indication which isspecific to the base station.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modein the wireless telecommunication system is applicable for a pluralityof base stations.

In accordance with certain embodiments the indication relates to theextent the base station supports the power boost operating mode in thewireless telecommunication system and does not relate to the extent anyother base station supports the power boost operating mode in thewireless telecommunication system.

In accordance with certain embodiments the indication relates to theextent at least one other base station supports the power boostoperating mode in the wireless telecommunication system.

In accordance with certain embodiments the terminal device is connectedto the base station and is not connected to the at least one other basestation.

In accordance with certain embodiments the method further comprisesreceiving from at least one further base station an indication of theextent to which the at least one further base station supports the powerboost operating mode in the wireless telecommunication system.

In accordance with certain embodiments the terminal device is notconnected to the base station at the time the indication of the extentto which one or more base stations support the power boost operatingmode is conveyed to the terminal device.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modeis implicitly conveyed to the terminal device in association withtransmissions made by the base station for communicating otherinformation.

In accordance with certain embodiments the step of conveying theindication of the extent to which one or more base stations support thepower boost operating mode in the wireless telecommunication systemcomprises transmitting broadcast signalling using transmission resourcesselected according to the indication to be conveyed.

In accordance with certain embodiments the broadcast signallingcomprises synchronisation signalling

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the power boost operating modeis conveyed to the terminal device using explicit signalling.

In accordance with certain embodiments the explicit signalling comprisessystem information signalling.

In accordance with another aspect of the disclosure there is provided amethod of operating a base station in a wireless telecommunicationsystem comprising one or more base stations which support a virtualcarrier operating mode in which at least some downlink communicationsare made using a restricted subset of transmission resources selectedfrom within a system frequency bandwidth and comprising a restrictedbandwidth downlink channel having a channel bandwidth which is smallerthan the system frequency bandwidth, the method comprising establishingan extent to which one or more base stations support the virtual carrieroperating mode; and conveying an indication of the extent to which oneor more base stations support the virtual carrier operating mode to aterminal device operating in the wireless telecommunication system sothe terminal device can take account of the indication of the extent towhich one or more base stations support the virtual carrier operatingmode for controlling its acquisition of a base station of the wirelesstelecommunication system.

In accordance with certain embodiments the indication relates to theextent at least one other base station supports the virtual carrieroperating mode in the wireless telecommunication system.

In accordance with certain embodiments the terminal device is connectedto the base station and is not connected to the at least one other basestation.

In accordance with certain embodiments the method further comprisesreceiving from at least one further base station an indication of theextent to which the at least one further base station supports thevirtual carrier operating mode in the wireless telecommunication system.

In accordance with certain embodiments the indication of the extent towhich one or more base stations support the virtual carrier operatingmode is conveyed to the terminal device using explicit signalling.

In accordance with certain embodiments the explicit signalling comprisessystem information signalling.

In accordance with another aspect of the invention there is provided abase station for use in a wireless telecommunication system comprisingone or more base stations which support a power boost operating mode inwhich a base station's available transmission power is concentrated toprovide enhanced transmission powers in a subset of its availabletransmission resources, wherein the base station is configured to:establish an extent to which one or more base stations support the powerboost operating mode; and, convey an indication of the extent to whichone or more base stations support the power boost operating mode to aterminal device operating in the wireless telecommunication system sothe terminal device can take account of the indication of the extent towhich one or more base stations support the power boost operating modefor controlling its acquisition of a base station of the wirelesstelecommunication system.

In accordance with another aspect of the disclosure there is provided abase station for use in a wireless telecommunication system comprisingone or more base stations which support a virtual carrier operating modein which at least some downlink communications are made using arestricted subset of transmission resources selected from within asystem frequency bandwidth and comprising a restricted bandwidthdownlink channel having a channel bandwidth which is smaller than thesystem frequency bandwidth, wherein the base station is configured toestablish an extent to which one or more base stations support thevirtual carrier operating mode and to convey an indication of the extentto which one or more base stations support the virtual carrier operatingmode to the terminal device operating in the wireless telecommunicationsystem so the terminal device can take account of the indication of theextent to which one or more base stations support the virtual carrieroperating mode for controlling its acquisition of a base station of thewireless telecommunication system.

It will be appreciated that features and aspects of the inventiondescribed above in relation to the first and other aspects of theinvention are equally applicable to, and may be combined with,embodiments of the invention according to other aspects of the inventionas appropriate, and not just in the specific combinations describedabove.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals and in which:

FIGS. 1A and 1B schematically show example plots of transmission powerversus frequency for two modes of operation for a base station in anLTE-based wireless telecommunication network operating at it maximumpermissible power output

FIG. 2 provides a schematic diagram illustrating an example of aconventional mobile telecommunication network;

FIG. 3 provides a schematic diagram illustrating a conventional LTEradio frame;

FIG. 4 provides a schematic diagram illustrating an example of aconventional LTE downlink radio subframe;

FIG. 5 provides a schematic diagram illustrating a conventional LTE“camp-on” procedure;

FIG. 6 schematically represents some elements of a wirelesstelecommunication system in accordance with some embodiments of theinvention;

FIG. 7 is a ladder diagram schematically representing some operationalaspects of elements of the wireless telecommunication system of FIG. 6in accordance with some embodiments of the invention;

FIG. 8 is a flow diagram schematically representing some operationalaspects of a terminal device in accordance with some embodiments of theinvention; and

FIG. 9 is a ladder diagram schematically representing some operationalaspects of elements of the wireless telecommunication system of FIG. 6in accordance with some embodiments of the invention;

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 2 provides a schematic diagram illustrating some basicfunctionality of a wireless telecommunications network/system operatingin accordance with LTE principles. Various elements of FIG. 2 and theirrespective modes of operation are well-known and defined in the relevantstandards administered by the 3GPP (RTM) body and also described in manybooks on the subject, for example, Holma, H. and Toskala, A. [1].

The network includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data are transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Dataare transmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.Terminal devices may also be referred to as mobile stations, userequipment (UE), user terminal, mobile radio, and so forth. Base stationsmay also be referred to as transceiver stations/nodeBs/e-NodeBs, and soforth.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division multiplex (OFDM) based interface for theradio downlink (so-called OFDMA) and a single carrier frequency divisionmultiplex based interface for the radio uplink (so-called SC-FDMA). FIG.3 shows a schematic diagram illustrating an OFDM based LTE downlinkradio frame 201. The LTE downlink radio frame is transmitted from an LTEbase station (known as an enhanced Node B) and lasts 10 ms. The downlinkradio frame comprises ten subframes, each subframe lasting 1 ms. Aprimary synchronisation signal (PSS) and a secondary synchronisationsignal (SSS) are transmitted in the first and sixth subframes of the LTEframe. A physical broadcast channel (PBCH) is transmitted in the firstsubframe of the LTE frame.

FIG. 4 is a schematic diagram of a grid which illustrates the structureof an example conventional downlink LTE subframe. The subframe comprisesa predetermined number of symbols which are transmitted over a 1 msperiod. Each symbol comprises a predetermined number of orthogonalsub-carriers distributed across the bandwidth of the downlink radiocarrier.

The example subframe shown in FIG. 4 comprises 14 symbols and 1200sub-carriers spread across a 20 MHz bandwidth. The smallest allocationof user data for transmission in LTE is a resource block comprisingtwelve sub-carriers transmitted over one slot (0.5 subframe). Forclarity, in FIG. 4, each individual resource element (a resource elementcomprises a single symbol on a single subcarrier) is not shown, insteadeach individual box in the subframe grid corresponds to twelvesub-carriers transmitted on one symbol.

FIG. 4 shows resource allocations for four LTE terminals 340, 341, 342,343. For example, the resource allocation 342 for a first LTE terminal(UE 1) extends over five blocks of twelve sub-carriers (i.e. 60sub-carriers), the resource allocation 343 for a second LTE terminal(UE2) extends over six blocks of twelve sub-carriers and so on.

Control channel data are transmitted in a control region 300 (indicatedby dotted-shading in FIG. 4) of the subframe comprising the first nsymbols of the subframe where n can vary between one and three symbolsfor channel bandwidths of 3 MHz or greater and where n can vary betweentwo and four symbols for channel bandwidths of 1.4 MHz. For the sake ofproviding a concrete example, the following description relates tocarriers with a channel bandwidth of 3 MHz or greater so the maximumvalue of n will be 3. The data transmitted in the control region 300includes data transmitted on the physical downlink control channel(PDCCH), the physical control format indicator channel (PCFICH) and thephysical HARQ indicator channel (PHICH).

PDCCH contains control data indicating which sub-carriers on whichsymbols of the subframe have been allocated to specific LTE terminals.Thus, the PDCCH data transmitted in the control region 300 of thesubframe shown in FIG. 4 would indicate that UE1 has been allocated theblock of resources identified by reference numeral 342, that UE2 hasbeen allocated the block of resources identified by reference numeral343, and so on.

PCFICH contains control data indicating the size of the control region(i.e. between one and three symbols).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Symbols in a central band 310 of the time-frequency resource grid areused for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 sub-carriers wide (corresponding to a transmissionbandwidth of 1.08 MHz). The PSS and SSS are synchronisation signals thatonce detected allow an LTE terminal device to achieve framesynchronisation and determine the cell identity of the enhanced Node Btransmitting the downlink signal. The PBCH carries information about thecell, comprising a master information block (MIB) that includesparameters that LTE terminals use to properly access the cell. Datatransmitted to individual LTE terminals on the physical downlink sharedchannel (PDSCH) can be transmitted in other resource elements of thesubframe.

FIG. 4 also shows a region of PDSCH containing system information andextending over a bandwidth of R₃₄₄. A conventional LTE frame will alsoinclude reference signals which are not shown in FIG. 4 in the interestsof clarity.

The number of sub-carriers in an LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 sub-carriers contained within a 20 MHz channel bandwidth (asschematically shown in FIG. 4). As is known in the art, data transmittedon the PDCCH, PCFICH and PHICH is typically distributed on thesub-carriers across the entire bandwidth of the subframe to provide forfrequency diversity. Therefore a conventional LTE terminal must be ableto receive the entire channel bandwidth in order to receive and decodethe control region.

FIG. 5 illustrates an LTE “camp-on” process, that is, the processfollowed by a terminal so that it can decode downlink transmissionswhich are sent by a base station via a downlink channel. Using thisprocess, the terminal can identify the parts of the transmissions thatinclude system information for the cell and thus decode configurationinformation for the cell.

As can be seen in FIG. 5, in a conventional LTE camp-on procedure, theterminal first synchronizes with the base station (step 400) using thePSS and SSS in the centre band and then decodes the PBCH (step 401).Once the terminal has performed steps 400 and 401, it is synchronizedwith the base station.

For each subframe, the terminal then decodes the PCFICH which isdistributed across the entire bandwidth of carrier 320 (step 402). Asdiscussed above, an LTE downlink carrier can be up to 20 MHz wide (1200sub-carriers) and an LTE terminal therefore has to have the capabilityto receive and decode transmissions on a 20 MHz bandwidth in order todecode the PCFICH. At the PCFICH decoding stage, with a 20 MHz carrierband, the terminal operates at a much larger bandwidth (bandwidth ofR₃₂₀) than during steps 400 and 401 (bandwidth of R₃₁₀) relating tosynchronization and PBCH decoding.

The terminal then ascertains the PHICH locations (step 403) and decodesthe PDCCH (step 404), in particular for identifying system informationtransmissions and for identifying its resource allocations. The resourceallocations are used by the terminal to locate system information and tolocate its data in the PDSCH as well as to be informed of anytransmission resources it has been granted on PUSCH. Both systeminformation and UE-specific resource allocations are transmitted onPDSCH and scheduled within the carrier band 320. Steps 403 and 404 alsorequire the terminal to operate on the entire bandwidth R₃₂₀ of thecarrier band.

At steps 402 to 404, the terminal decodes information contained in thecontrol region 300 of a subframe. As explained above, in LTE, the threecontrol channels mentioned above (PCFICH, PHICH and PDCCH) can be foundacross the control region 300 of the carrier where the control regionextends over the range R₃₂₀ and occupies the first one, two or threeOFDM symbols of each subframe as discussed above. In a subframe,typically the control channels do not use all the resource elementswithin the control region 300, but they are scattered across the entireregion, such that a LTE terminal has to be able to simultaneouslyreceive the entire control region 300 for decoding each of the threecontrol channels.

The terminal can then decode the PDSCH (step 405) which contains systeminformation or data transmitted for this terminal.

As explained above, in an LTE subframe the PDSCH generally occupiesgroups of resource elements which are neither in the control region norin the resource elements occupied by PSS, SSS or PBCH. The data in theblocks of resource elements 340, 341, 342, 343 allocated to thedifferent mobile communication terminals (UEs) shown in FIG. 4 have asmaller bandwidth than the bandwidth of the entire carrier, although todecode these blocks a terminal first receives the PDCCH spread acrossthe frequency range R₃₂₀ to determine if the PDCCH indicates that aPDSCH resource is allocated to the UE and should be decoded. Once a UEhas received the entire subframe, it can then decode the PDSCH in therelevant frequency range (if any) indicated by the PDCCH. So forexample, UE 1 discussed above decodes the whole control region 300 andthen the data in the resource block 342.

As noted above, it is expected that certain terminal devices might be inlocations with relatively high penetration loss as regards radiocommunications with a base station. For example, an MTC-type terminaldevice associated with a smart meter application may be located in abasement. This can mean certain devices may require a base station totransmit with significantly higher power levels than for other terminaldevices coupled to the base station in order to support reliablecommunications. Although it may be expected that MTC type terminaldevices might often be in “harder to reach” locations than other typesof terminal device, it will be appreciated the issues relating tocoverage extension as discussed herein can equally apply to non-MTC typeterminal devices. As schematically represented in FIG. 1B and discussedabove, one proposal for reliably supporting communications with terminaldevices in areas of relatively poor coverage without simply increasingthe overall transmission power from a base station is to focus a basestation's transmission budget into relatively high powered transmissionsin a subset of frequencies spanning a bandwidth which is less than thenormal operating bandwidth for the base station. However, as also notedabove, a terminal device seeking to camp on/access a particular basestation in accordance with conventional techniques will generally beunaware of the circumstances in which the base station can support powerboosting until the terminal device has been able to decode relativelyhigh-level system information associated with the base station. That isto say, the terminal device must undergo the process of FIG. 5 beforedetermining whether or not the base station can in fact reliably supportcommunications with the terminal device in a power-boosted mode ofoperation. Certain embodiments of the invention are directed to schemesfor providing terminal devices with information on base stations'capabilities to operate in a power boosting mode (e.g. in terms ofif/when a base station supports power boosting) with a view to reducingwasted camp on attempts.

FIG. 6 is a schematic diagram showing part of a telecommunicationssystem 1400 arranged in accordance with an example of the presentinvention. The telecommunications system 1400 in this example is basedbroadly on an LTE-type architecture. As such many aspects of theoperation of the telecommunications system 1400 are known and understoodand are not described here in detail in the interest of brevity.Operational aspects of the telecommunications system 1400 which are notspecifically described herein may be implemented in accordance with anyknown techniques, for example according to the current LTE standards.

Represented in FIG. 6 are three communication cells 1404A, B, Csupported by respective base stations 1401A, B, C coupled to a corenetwork 1408. The communication cells are nominally represented in FIG.6 as adjacent hexagons, but it will be appreciated in practice therespective coverage areas associated with the different base stationswill overlap such that an individual terminal device may be locatedwithin the nominal geographic footprint of more than one base station.For example, it is assumed here a terminal device 1403 in accordancewith an embodiment of the invention happens to be at a location which iswithin the nominal coverage areas of all three base stations 1401A, B,C. This is schematically shown in FIG. 6 by the terminal device 1403being represented at a point where the three hexagons schematicallyrepresenting the three communication cells 1404A, B, C meet.Accordingly, the terminal device 1403 may in principle access (i.e.connect to or camp on) any of the base stations 1401A, B, C. Inaccordance with common practice, the terms base station and cell maysometimes be used herein interchangeably, for example, the process of aterminal device connecting to the radio access part of a wirelesstelecommunications system might be referred to as accessing a cell oraccessing a base station.

It will be appreciated that in general a system such as that representedin FIG. 6 will comprise a greater number of cells arranged to providecoverage over a more extended geographic area. As is conventional forLTE-type networks, the respective base stations 1401A, B, C maycommunicate with one another over the so-called X2 interface whichinterconnects base stations in a peer-to-peer fashion.

For the sake of a concrete example, it will be assumed here the two basestations 1401A, 1402B are configured to support a power boosting mode ofoperation while the base station 1401C is not configured to support apower boosting mode of operation.

Referring to FIG. 6, communication cell 1404A thus includes base station(enhanced Node B/eNB) 1401A connected to the core network 1408. The basestation 1401A comprises a transceiver unit 1410A for transmission andreception of wireless signals and a controller unit 1411A configured tocontrol the base station 1401A. The controller unit 1411A may comprisevarious sub-units, such as a scheduling unit 1409A and other functionalunits for providing functionality in accordance with embodiments of theinvention as explained further below. These sub units may be implementedas discrete hardware elements or as appropriately configured functionsof the controller unit. Thus, the controller unit 1411A may comprise aprocessor unit which is suitably configured/programmed to provide thedesired functionality described herein using conventionalprogramming/configuration techniques for equipment in wirelesstelecommunications systems. The transceiver unit 1410A and thecontroller unit 1411A are schematically shown in FIG. 6 as separateelements for ease of representation. However, it will be appreciatedthat the functionality of these units can be provided in variousdifferent ways following established practices in the art, for exampleusing a single suitably programmed integrated circuit coupled to anantenna. It will be appreciated the base station 1401A will in generalcomprise various other elements associated with its operatingfunctionality.

The base station 1401A may communicate with a plurality of conventionalLTE terminals 1402A within the coverage area of the cell 1404A inaccordance with conventional techniques. The base station 1401A isarranged to transmit downlink data using a subframe structure thatfollows that schematically represented in FIG. 4, and furthermore, thismay be done in either a normal operating mode or a power boostedoperating mode as discussed above and schematically represented in FIGS.1A and 1B.

As noted above, it is assumed here for the sake of a concrete examplethe base stations 1401A, 1401B associated with communication cells1404A, 1404B both support a power boosted mode of operation, whereas thebase stations 1401C associated with communication cells 1404C does not.The various elements and functionality associated with the communicationcell 1404B are thus in essence the same as for the communication cell1404A. Similarly, the various elements and functionality associated withthe communication cell 1404C are in essence the same as for thecommunication cell 1404A (except the base station 1401C of communicationcell 1404C is assumed in this example to not support the power boostedmode of operation). With this in mind, it will be appreciated thevarious elements of communication cells 1404B, 1404C represented in FIG.6 will be similar to, and will be understood from, the correspondingelements of communication cell 1404A (except for the inability of basestation 1401C to support power boosted transmissions).

As noted above, a terminal device 1403 in accordance with an embodimentof the invention is also represented in FIG. 6 at a location within thenominal geographic footprint of each of the three communication cells1404A, B, C associated with the three base stations 1401A, B, C. Theterminal device 1403 may be based around any conventional terminaldevice with adaptions to support operation in accordance withembodiments of the invention as described herein.

The terminal device 1403 comprises a transceiver unit 1405 fortransmission and reception of wireless signals and a controller unit1407 configured to control the device 1403. The controller unit 1407 maycomprise various sub-units for providing functionality in accordancewith embodiments of the invention as explained herein. These sub unitsmay be implemented as discrete hardware elements or as appropriatelyconfigured functions of the controller unit. Thus the controller unit1407 may comprise a processor unit which is suitablyconfigured/programmed to provide the desired functionality describedherein using conventional programming/configuration techniques forequipment in wireless telecommunications systems. The transceiver unit1405 and the controller unit 1407 are schematically shown in FIG. 6 asseparate elements for ease of representation. However, it will beappreciated that the functionality of these units can be provided invarious different ways following established practices in the art, forexample using a single suitably programmed integrated circuit. It willbe appreciated the terminal device 1403 will in general comprise variousother elements associated with its operating functionality. Operationalaspects of the terminal device 1403 which are not described herein maybe implemented in accordance with conventional techniques.

A mode of operation whereby the terminal device 1403 controls itsacquisition of one of the base stations 1401A, B, C of the wirelesstelecommunications system 1400 in accordance with an embodiment of theinvention will now be described. The base station 1401C is assumed inthis example to not support a power boosted operating mode, and as suchthe operation of this base station may be entirely conventional.

Various examples will be described in which a terminal device controlsits acquisition of a base station of a wireless telecommunicationssystem based on information received from one or more base stationsregarding the extent to which one or more base stations in the wirelesstelecommunications system support a power boosted mode of operation. Inthis respect controlling acquisition may be considered to correspondwith controlling a camp-on/cell-attach procedure through which aterminal device receives signalling from a particular base station. Theterms acquire and access (and derivatives thereof) may sometimes be usedinterchangeably throughout this description and should be interpretedaccordingly unless the context demands otherwise. In some cases, forexample when a terminal device is first switched on, the acquisition maycorrespond with a cell selection procedure. In other cases, for examplewhere a terminal device is to camp on a different base station, the stepof controlling acquisition may correspond with controlling a cellreselection or handover procedure.

By taking account of different base stations' capabilities with regardto the power boosted mode of operation a terminal device may be able tomore efficiently control its acquisition of a base station in accordancewith embodiments of the invention. For example, if a terminal devicerelies on power boosting to reliably receive data it might avoidattempting to attach to base stations which do not support a powerboosted mode of operation and/or might delay accessing a base stationuntil a later time when power boosting is available for the basestation.

In a first example it will be assumed the terminal device 1403 has justbeen switched on, and needs to determine which of the available basestations 1401A, 1401B, 1401C it will access/camp on. In accordance withstandard techniques, a terminal device which is within the coverage areaof multiple cells will in these circumstances typically undertakemeasurements of signalling received from the different cells toestablish a measure of radio link conditions for communications fromeach base station and access one of the base stations based on themeasured radio link conditions. However a drawback of this approach isthat the terminal device is unaware of the extent to which radio linkconditions may be improved because of the availability of powerboosting. Thus, in accordance with certain embodiments of the inventionterminal devices may receive an indication of the extent to which basestations in the wireless telecommunications network support powerboosting to assist in the process of accessing the network through anappropriate base station.

In some embodiments the individual base stations which support the powerboosted mode of operation are each configured to implicitly convey theirown indication of the extent to which they support the power boost modeto terminal devices. In some examples the indication may be conveyed inassociation with broadcast signalling received by terminal devices inidle mode. For example, in some cases an indication of the extent towhich a base station supports a power boosted mode (i.e. an indicationof power boost availability (PBA)) may be implicitly conveyed accordingto the transmission resources selected by the base station inassociation with broadcast signalling, such as synchronisationsignalling. The power boost availability (PBA) indication might, forexample, indicate the level, times of availability, or simply theexistence, of power boosting for particular base stations. As alreadynoted, this information can help a terminal device control itsacquisition of a base station, for example by governing how the terminaldevice conducts and responds to signal measurements for cellselection/re-selection, as well as for handover, in order to takeaccount of the potentially improved suitability of a cell that supportspower boosting, as well as governing how a terminal device might enter asleep mode before waking up to connect to a cell for which a PBAindication indicates better coverage might be available at someparticular time of day.

More generally, by taking account of different base stations'capabilities with regard to the power boosted mode of operation aterminal device is able to more efficiently control its acquisition ofbase stations, for example by avoiding attempting to attach to a basestation which does not support a power boosted mode of operation if theterminal device requires the power boosted mode of operation to reliablyreceive data, or by delaying a procedure for accessing a base stationuntil a time when power boosting is indicated as being available for thebase station. In this respect controlling access may be considered tocorrespond with controlling a camp-on/cell-attach procedure throughwhich a terminal device connects to a particular base station. In somecases, for example when a terminal device is first switched on, theaccess may correspond with a cell selection procedure. In other cases,for example where a terminal device is to move to a different basestation, the access may correspond with a cell reselection procedure.

In one example embodiment a base station may provide for repetitions ofsynchronisation signalling sequences, such as the primarysynchronisation sequences (PSS) and secondary synchronisation sequences(SSS) employed in LTE-type networks. As noted above, synchronisationsignalling is provided on certain specified transmission resourcesaccording to the implemented standard to help a terminal device whichhas just switched on to easily locate the synchronisation signalling,thereby allowing the terminal device to more rapidly synchronise totransmissions from the base station to help the acquisition of furthersignalling associated with connecting to a network.

Co-pending UK patent application numbers GB 1305233.7—filed 21 Mar. 2013[2] and GB 1350234.5—filed 21 Mar. 2013 [3] disclose mechanisms forconveying information regarding a range of Physical Cell Identities(PCI) and/or SSS values that a terminal device searches. This isachieved by varying the subframes or OFDM symbols in which someadditional repetition(s) of PSS/SSS occur. A similar approach could betaken in accordance with an embodiment of the invention in which basestation wishing to broadcast a particular PBA indication may do so byselecting an appropriate format of synchronisation signalling repetitionaccording to the information to be conveyed. For example, in a simplecase the network may allow base stations to simply indicate whether ornot the base station is currently able to adopt the power boosted mode.A base station may in effect advertise its capabilities in this respectby introducing a repetition of synchronisation signalling at apre-specified location in its downlink subframe, for example at aparticular time and/or frequency offset relative to conventionalsynchronisation signalling. A terminal device detecting such arepetition may therefore conclude the base station is advertising itsability to operate in a power boosted mode and take this informationinto account when taking decisions on how the terminal device is toaccess the network. It may be noted that a terminal device whichrequires power boosting to reliably receive, for example, the physicaldownlink shared channel (PDSCH) in a wireless telecommunications systemmay nonetheless be able to reliably receive other signalling, such assynchronisation signalling, since this is generally transmitted with asignificantly higher degree of redundancy than PDSCH transmissions.Thus, it may be expected that a terminal device which is in a locationwhich makes it difficult to reliably receive PDSCH transmissions maynonetheless reliably receive other signalling.

Different mappings between transmission resources used for broadcastsignalling and information regarding power boost capabilities may beestablished according to a standard. For example, different locations(in the time/frequency domain) for synchronisation signallingrepetitions may be associated with different information to be conveyedregarding the extent to which one or more base stations support a powerboost mode of operation. A base station may thus establish the extent towhich it (or other base stations as discussed further below) is tosupport the power boost mode, this may be a fixed characteristic of thebase station or determined dynamically, for example according to howmuch disruption the power boost mode of operation would cause for otherusers of the network, and convey this information implicitly byappropriately selecting transmission characteristics for broadcastsignalling, such as synchronisation signalling, according to apre-established mapping between transmission characteristic andinformation to be conveyed. As will be appreciated, more “bits” ofinformation (different states) can be communicated by increasing thenumber of different options a base station may choose from with regardsto its broadcast signalling. For example, allowing for potentially morerepetitions of synchronisation signalling provides a correspondinglygreater number of states that can be distinguished for indicatingdifferent extents of power boost availability. A terminal deviceexpecting to need coverage extension on PDSCH/PDCCH to operate reliablycan simply choose not to connect to a cell associated with an indicationof insufficient availability of power boosting. This saves power at theterminal device and can reduce uplink interference (and thereforere-transmissions) on PRACH since there is a corresponding reduction interminal devices attempting to acquire cells that are unable to supporttheir power boosted needs.

As noted above, a PBA indication may be selected by a base station toconvey various types of information regarding the extent to which one ormore base stations support power boosting in the network. For example,depending on the implementation, a PBA indication conveyed from a basestation to terminal devices may in accordance with some embodiments beused to indicate one or more of the following:

(i) the availability of any power boosting for one or more basestations;(ii) the level of any power density boost that is available, for examplethe power enhancement (e.g. in dB) that is available for resources onwhich power boosted transmissions may be made relative to thedefault/nominal power levels available without power boosting.(iii) time(s) when power boost (or an amount of power boost) can beexpected to be available. This could, for example, be based on a fairlycoarse division of each day into segments to match the available numberof states of the PBA indication mechanism for a given implementation. Inone simple example the extent to which a base station supports powerboosting may correspond with supporting power boosting at a high boostlevel (power enhancement) between 00:00-05:30, supporting power boostingat a low boost level between 22:00-00:00, and not supporting any powerboosting between 05:30-22:00. This extent of power boost support couldbe conveyed to a terminal device with a three-states PBA indication. Thespecific meanings in such a case for ‘high’ and ‘low’ (e.g. in terms ofactual power level enhancement) could be established in various ways,for example it could be agreed between network operators and terminaldevice manufacturers outside a standard specification, or it could bewritten into a standard's specifications.(iv) on which downlink physical channels power boosting is available(for example, where power boosting may be supported on some downlinkphysical channels, but not others).

Methods of operation of elements of the wireless telecommunicationssystem 1400 represented in FIG. 6 in accordance with some embodiments ofthe invention will now be described. In the first examples to bedescribed it will be assumed the terminal device 1403 is initially notconnected (attached/camped-on) to any base station.

As is conventional for LTE-type networks, a terminal device in RRC_IDLEmode detects the presence of available base stations/cells and measurestheir RSRP/RSRQ levels. Based on these measurement results, a basestation is selected to which the terminal device will attempt to attachfrom rankings based on the measurement. Terminal devices use theselected base station/cell for various terminal device procedures, suchas receiving paging messages, reading system information (SI), andeventually random access procedures, for example when the terminaldevice is to move to RRC_CONNECTED mode.

Typically, initial cell selection is performed immediately after aterminal device is powered on. In accordance with standard techniques, anewly switched on terminal device starts to scan its supported bands andselect a cell to camp-on based on its preferred operator's network (i.e.PLMN identity in its SIM card) and terminal device measurement resultsaccording to established cell selection procedure. Further details onthese procedures in the context of an LTE-type network can be found, forexample, in the 3GPP document ETSI TS 136 304 V11.2.0 (2013-02)/3GPP TS36.304 Version 11.2.0 Release 11 [4]

Later cell selection procedures after an initial cell selectionprocedure are sometimes called “cell reselection” procedure is in LTE.With cell reselection, a terminal device looks for neighbouring cellswith better RSRP/RSRQ than its currently-selected cell. The reselectioncriteria/procedure is considered a separate procedure from (initial)cell selection, but in many respects the principles described hereinapply equally for both types of procedure. Further details on cellreselection procedures in the context of an LTE-type network can also befound in ETSI TS 136 304 V11.2.0 (2013-02)/3GPP TS 36.304 Version 11.2.0Release 11 [4].

As mentioned above the amount of information to be conveyed to terminaldevices regarding base stations' capabilities as regards a power boostoperating mode may be different in accordance of differentimplementations. Some examples may employ a simple one-bit indication ofwhether or not power boosting is available in the cell at all (forexample at a fixed predefined level), and this may be referred to as a‘single-level’ indication. A single level indication for a given basestation may be provided, for example, according to whether or not thebase station is broadcasting a synchronisation signalling repetition ona particular transmission resources defined for this purpose. Some otherexamples may convey more than one-bit of information. For example, theindication of the extent to which a base station supports power boostingmight include an indication of which of a number of possible differentlevels of power boost are being offered by a cell, and this may bereferred to as a ‘multi-level’ indication. The latter may arise, forexample, if a cell can change its power boost over time, or if thenetwork as a whole supports more than one power boost level, andper-cell PBA-level indication is therefore desired.

Based on the above two characteristics four different cases may beconsidered for an idle mode terminal device, namely:

-   -   Cell selection with single-level PBA indication    -   Cell selection with multi-level PBA indication    -   Cell re-selection with single-level PBA indication    -   Cell re-selection with multi-level PBA indication

Examples of these different cases will now be described. However, aswill be appreciated the underlying principles of operation are to largeextent the same for each case. In each case it is assumed the terminaldevice 1403 make use of information received from one or more of thebase stations represented in FIG. 6 regarding the extent to which thevarious base stations support power boosting.

FIG. 7 is a ladder diagram schematically representing some operationalaspects of the terminal device 1403 and the base stations 1401A, B, C ofFIG. 6 for an example of initial cell selection with single PBAindication in accordance with an embodiment of the invention. The PBAindication is thus provided simply to identify whether or not the basestation supports power boosting. The level of power boosting, forexample in terms of a potential power increase in dB for thetransmission resources in which power is concentrated when powerboosting, may be predefined in accordance with the standards. Forexample, operating standards associated with the wirelesstelecommunications system may specify a power boosting mode ascomprising a four-fold increase in available power (around 6 dB) withinone quarter of the available transmission resources.

Thus, in a first step the terminal device wakes up, for example oninitial switch on/after a quiescent period. In accordance withconventional LTE principles, the terminal device scans forsynchronisation signalling being broadcast by surrounding base stations.As noted above, it is assumed for the example of FIG. 6 the terminaldevice is within the nominal coverage area of all three base stations1401A, B, C. Thus, and as schematically represented in FIG. 7, theterminal device is able to receive primary (PSS) and secondary (SSS)signalling from each of the base stations. In accordance with theprinciples described above, the respective base stations which supportpower boosting are configured to indicate this by making transmissionsin association with their synchronisation signalling (e.g. signallingrepetitions) on transmission resources specifically defined for thispurpose. This is schematically represented in FIG. 7 for the basestations which support power boosting (i.e. base stations 1401A and1401B) by the labelling “[PB]” associated with the representation oftheir PSS/SSS signalling. A base station which does not support powerboosting (such as base station 1401C) does not make transmissionsassociated with synchronisation signalling on the pre-definedtransmission resources, thereby in effect indicating its inability touse power boosting.

The terminal device 1403 is configured to search for synchronisationsignalling repetitions on the transmission resources defined forindicating the availability of power boosting, and if suchsynchronisation signalling is found, the terminal device 1403 determinesthe corresponding base station supports power boosting. Thus theterminal device 1403 determines that the base stations 1401A and 1401Bsupport power boosting, whereas the base station 1401C does not. Thus,the terminal device 1403 reaches a stage at which it has identified whatbase stations are in range and which of them support power boosting.

In the next two stages represented in FIG. 7, the terminal device 1403establishes which base stations correspond with its preferred (priority)PLMN and makes RSRP measurements for each base station. Here it isassumed that all three base stations correspond with the terminaldevice's preferred PLMN, and so RSRP measurements are undertaken foreach base station/cell. These two stages may be performed in accordancewith conventional techniques.

Having obtained the RSRP measurements, and taking account of theinformation previously-received regarding the extent to which thevarious base station support power boosting, the next stages ofoperation for the terminal device 1403 represented in FIG. 7 are a cellranking stage and a cell selection stage. In these stages the terminaldevice controls how it will subsequently access a base station of thewireless telecommunications system by determining which of the availablebase stations is most appropriate for connecting to, taking account ofthe RSRP measurements and abilities to support power boosting for therespective base stations.

In general, the cell ranking stage may follow the same generalprinciples as for a conventional cell attach procedure, except that inaddition to taking account of the RSRP measurements, account is alsotaken of the extent to which the base station support power boosting.One way to do this is to in effect uprate the RSRP measurements for basestations which support power boosting. For example reference signalreceived power measurements (RSRP) for base stations which support powerboosting may be replaced for the purpose of cell ranking with a modifiedRSRP corresponding to the measured RSRP plus and offset corresponding tothe available power boosting enhancement. For example, if thespecification defines power boosting as corresponding to a 6 dBenhancement, the RSRP measurements for base stations which indicate theysupport power boosting may be increased by 6 dB. The modified RSRP thusreflects the channel characteristics that may be achievable when powerboosting is active for a given base station.

For example, if the terminal device 1403 were to determine the RSRPmeasurements for base station 1401C (which does not support powerboosting) were 2 dB higher than for base station 1401A (which doessupport power boosting) and 3 dB higher than for base station 1401B(which also supports power boosting), the terminal device would inaccordance with conventional cell selection techniques determine thatbase station 1401C should be preferred for the purposes of accessing thenetwork. However, in accordance with an embodiment of the invention, theterminal device can recognise at this early stage in the attachprocedure that base station 1401A in fact has the potential for higherreceived signal powers because it has provided an indication of thepotential for a 6 dB power enhancement through power boosting. Thus, inaccordance with an embodiment of the invention, the terminal device mayinstead determine that base station 1401A is in fact the first basestation through which to access the network. This is schematicallyrepresented in FIG. 7 by the indication that cell A is selected at thecell selection stage.

Having selected a base station (cell) through which to access thenetwork in accordance with an embodiment of the invention, the terminaldevice 1403 may proceed in line with conventional techniques. Thus, asschematically represented in FIG. 7, the base station may proceed toreceive and decode the physical broadcast channel (PBCH) transmitted bythe selected base station, in this case base station 1401A serving cell1404A, and follow the remainder of the camp on procedure schematicallyrepresented in FIG. 5 to derive system information, and so forth.

Thus, in accordance with the techniques described above with referenceto FIG. 7, the terminal device is able to avoid undertaking anunnecessary camp on procedure for base station 1401C which might happento be associated with the highest RSRP, but which ultimately may not beable to reliably support communications with the terminal device becauseit does not support power boosting.

FIG. 8 is a flow diagram schematically representing some aspects of theoperation of the terminal device 1403 in accordance with animplementation of an embodiment of the invention as described above withreference to FIG. 7. Steps S2 to S6 are shown as representing stepsassociated with one base station, but it will be appreciated thatcorresponding steps are performed for other base stations that are inrange of the terminal device. Steps corresponding to steps S2 to S6 maythus be performed for multiple base stations, either in series, parallelor interleaved manner.

Processing starts in a step S1, for example when the terminal device isinitially switched on.

In step S2 the terminal device detects synchronisation signalling from abase station in range.

In step S3 the terminal device determines whether the signallingreceived from the base station comprises an indication of anavailability of power boosting.

In step S4 the terminal device determines a power boost levelcorresponding to the extent to which power boosting is indicated asbeing available for the base station. For example, if no power boostindication is associated with the synchronisation signalling for thisparticular base station, the terminal device may identify there is 0 dBpower boost available for the base station (e.g. as for base station1401C in FIG. 6). If, on the other hand, the terminal device determinesthere is an indication that the base station supports power boosting,the indication may be converted into a corresponding power boost level.For example, a fixed potential power boost level of 6 dB in the case ofthe example provided above. The power boost level may, for example bereferred to as an offset.

In step S5 the terminal device undertakes RSRP measurements for the basestation.

In step S6 the terminal device adjusts the measured RSRP for the basestation to take account of the potential power boost enhancement(offset) established in step S4. For example, a modified RSRPcorresponding to the measured RSRP plus the available power boost levelmay be determined.

In step S7 the terminal device determines from reference signallingmeasurements, taking account of any potential improvement from powerboosting, whether or not the base station base station meets certainminimum requirements for selection. If a base station fails to meetthese requirements, it may be discounted from any further consideration.If, on the other hand, a base station meets these requirements, it mayremain as a candidate for selection. The minimum selection criterion maybroadly correspond with those applied in a conventional LTE networks butmodified to take account of what, if any, power boosting is indicated asavailable for the base station under consideration.

Thus, a base station may be considered to meet the minimum selectioncriterion if both the following inequalities are satisfied:

RSRP+Offset>(Q _(rxlevmin) +Q _(rxlevminoffset))+P_(compensation)  (Eqn. 1)

RSRQ+Offset>(Q _(qualmin) +Q _(qualminoffset))  (Eqn. 2)

It will be recognised these inequalities closely correspond with testsapplied for cell selection in a conventional LTE type network, forexample as described in the 3GPP document ETSI TS 136 304 V11.2.0(2013-02)/3GPP TS 36.304 Version 11.2.0 Release 11 [4]. In each case, itis only the left-hand side of the inequality that is different. For aconventional LTE approach the left-hand side of these inequalities wouldrespectively correspond simply to RSRP (for Equation 1) and RSRQ (forEquation 2), whereas in accordance with embodiments of the invention,the left-hand side of the inequalities are modified to take account ofthe potential improvements (offsets) associated with the level of theavailable power boosting. For example in both cases the offset might be6 dB in accordance with an embodiment of the invention. The variousparameters listed on the right hand side of the above inequalities aredefined in the relevant standards, for example in 3GPP TS 36.304 Version11.2.0 Release 11 [4] where they are defined according to the followingtable (see Section 5.2.3.2):

Srxlev Cell selection RX level value (dB) Squal Cell selection qualityvalue (dB) Q_(rxlevmeas) Measured cell RX level value (RSRP)Q_(qualmeas) Measured cell quality value (RSRQ) Q_(rxlevmin) Minimumrequired RX level in the cell (dBm) Q_(qualmin) Minimum required qualitylevel in the cell (dB) Q_(rxlevminoffset) Offset to the signalledQ_(rxlevmin) taken into account in the Srxlev evaluation as a result ofa periodic search for a higher priority PLMN while camped normally in aVPLMN [5] Q_(qualminoffset) Offset to the signalled Q_(qualmin) takeninto account in the Squal evaluation as a result of a periodic searchfor a higher priority PLMN while camped normally in a VPLMN [5]Pcompensation max(P_(EMAX)-P_(PowerClass), 0) (dB) P_(EMAX) Maximum TXpower level an UE may use when transmitting on the uplink in the cell(dBm) defined as P_(EMAX) in [6] P_(PowerClass) Maximum RF output powerof the UE (dBm) according to the UE power class as defined in [6]

Although Equations 1 and 2 show the left-hand sides of the inequalitiesbeing increased by the relevant offset, the same test result can ofcourse be achieved by having the right hand sides reduced by therespective offsets.

In step S8 the terminal device in effect ranks the various base stationsthat have been considered and which meet the quality test of step S7according to the modified values of RSRP (i.e. measured RSRP plus thelevel of available power boosting offset). Thus, the terminal device mayselect the base station for which the modified RSRP value is highest asthe base station with which the terminal device is to continue an attachprocedure.

In step S9 the terminal device proceeds with attaching to the selectedcell/base station. Once the desired cell is selected, the attach (campon) procedure may continue as normal.

It will be appreciated that in other embodiments of the processingrepresented in FIGS. 7 and 8 may be subject to modification. Forexample, in some implementations it may be decided that a terminaldevice should never attempt to camp on a base station that does notsupport power boosting. In this case, if a terminal device determines ina step corresponding to step S3 in FIG. 8 that no power boosting isavailable for a particular base station, the base station may bediscarded from any further consideration.

Thus, in accordance with an embodiment of the invention as describedabove, a terminal device is provided with an early indication of theextent to which base stations to which the terminal device may considerattaching support power boosting, thereby allowing the terminal deviceto take account of this information when determining the mostappropriate base station through which to connect to the network.

While the example represented in FIGS. 7 and 8 is in effect based arounda single bit indication regarding the extent to which base stationsupport power boosting (i.e. whether not they do support powerboosting), in other examples more information may be conveyed. As notedabove, this may be referred to as a multi-level approach. For example,in accordance with certain embodiments different base stations maysupport different levels of power boosting. For example, one basestation may only allow for power boosting up to 3 dB, while another basestation may allow power boosting up to 9 dB. Different predefinedarrangements of transmission resources for broadcast signallingrepetitions may be associated with different power boost levels. Thus, abase station can establish the extent to which it will support powerboosting (for example whether at 3 dB or at 9 dB, or whichever othervalues might be available for a given implementation), and convey thisto terminal devices through an appropriate selection of transmissionresources for synchronisation signalling. For example, one approach mayallow for four states of power boost availability to be indicated (e.g.based on the selective presence or absence of two signallingrepetitions) corresponding to power boost levels of 0 dB, 3 dB, 6 dB and9 dB. Individual base stations may establish the power boost level theyare to support either based on fixed configuration information, ordynamically based on current traffic. For example a relatively congestedbase station may determine that it should not apply any power boostingbecause this will reduce its ability to serve other terminal devices.However, a base station which is relatively lightly loaded may determinethat it can operate using the maximum power boost mode for certainterminal devices without significantly impacting its overall operationfor other terminal devices.

A multi-level approach may follow generally the approach of FIGS. 7 and8 except the terminal device may determine a different power boostenhancement/offset for different base stations according to theindications provided in association with their synchronisationsignalling. The cell ranking procedure may then correspondingly takeaccount of the different power boost levels available for the differentbase stations when determining the most appropriate base station toaccess and whether particular base stations are able to meet the minimumselection requirements.

The examples described above with reference to FIGS. 7 and 8 haveprimarily focused on an initial cell acquisition process (cellselection). However, as noted above, broadly similar principles canapply during a cell reselection process. For example when an idle modeterminal device is already camped on an initial cell/base station, itmay be appropriate to consider moving to another cell, for examplebecause the quality of signalling associated with the initial cell hasdeteriorated. A terminal device may perform a cell reselection proceduretaking account of the extent to which different base stations offerpower boosting using what are in effect the same selection processes asdescribed above for initial cell selection. However, it may also benoted that for cell reselection the terminal device has already campedon to a base station of the network and so will have had access tosystem information. Thus in accordance with some embodiments of theinvention, information conveyed in system information may be used toprovide an indication of the extent to which different base stationssupport power boosting in the network to assist terminal devices controltheir acquisition of base stations. This type of approach may beprovided in conjunction with the implicit signalling approach describedabove or may be provided on its own independently of an implicitapproach.

Thus, in accordance with some embodiments the concept of a list of whichbase stations support power boosting within a wirelesstelecommunications system, and potentially characteristics of the powerboosted they offer, for example in terms of power boost level, timesduring which power boosted available, and so forth, may be introduced.This may conveniently be referred to as a white list for power boostavailability. The list may, for example, be broadcast by the basestation in association with system information normally received byterminal devices attached to the base station. Thus, terminal deviceswhich are already connected to a station may be readily provided withinformation regarding the extent to which other base stations in thenetwork support power boosting. This information can assist terminaldevices determine whether to move to another base station by allowingterminal devices to take account of what improvements in radio linkconditions might be expected to be achievable over measured channelconditions for various base stations according to the availability ofpower boosting. The following table represents an example power boostavailability white list linking communication cell identities (PCIs) toexample levels of power boost supported by the respective cells.

Cell ID power boost 43 3 dB 432 6 dB 124 9 dB 156 6 dBEach base station may be configured to maintain the white list forcommunication to their connected terminal devices. The list may bemaintained (semi)dynamically based on communications between basestations regarding their intended support for power boosting, forexample using the X2 interface between base stations using newly-definedextra information elements. For an example, individual base stations maycommunicate to neighbouring base stations using X2 signalling when theychange their support for the power boosted mode. Alternatively, the listmay be (semi)static based on an operator selected network configuration.Thus, when a terminal device in idle mode measures the RSRP/RSRQ of CellID 432 it may modify the measurements to account for the potential 6 dBpower boost improvement offered by cell ID 432, and so forth.

Thus, in accordance with some embodiments, a serving cell to which aterminal device has already connected may provide a PBA indicationrelevant for a neighbouring cell or cells. If a terminal device isconnected to the serving cell (possibly, but not necessarily, afterdeciding to connect in a manner taking account of indications of powerboost availability such as described above), RRC configurationsignalling can be used to convey PBA indications relevant for other basestation(s)/cell(s). A terminal device can then use this information tojudge whether, and potentially when, to try to acquire a neighbouringcell. The terminal device may, for example, determine that it would bepreferable to abandon the serving cell and attach to a neighbour cell ifthe neighbour is reported as being able to offer better service takingaccount of the availability of power density boosting. This could beachieved through an explicit request made to the currently serving cellwhich could then initiate a handover (HO) procedure or, if uplinkcoverage is too poor in the serving cell, by simply commencing a newcell acquisition procedure on the neighbour cell.

In a variation of this approach where PBA indications containinformation regarding the time(s) of day at which one or more basestations/cells can offer power density boosting, a terminal device maycontrol its access to the network by deciding to enter a power savingstate, perhaps amounting to a switch-off, until a time at which powerdensity boosting is available. The terminal device can then wake up atthe relevant time and connect to the power-boosting cell. This couldrepresent a significant power saving advantage for the terminal device.As noted above, neighbour cell PBA information can also be provided toidle terminal devices by including relevant information in the SystemInformation (SI) broadcasts. Idle-mode terminal devices checkperiodically for SI changes by checking a configured pattern ofsubframes for a paging PDCCH which identifies the PDSCH resources inwhich the SI is held in the subframe. This provides a mechanism for idlemode terminal devices to receive explicit signalling regarding one ormore base stations' capabilities as regards power boosted operation

It may be noted that in principle a particular cell identity could beassociated with a negative power boost level. This would have the effectof discouraging terminal devices from camping on to this cell even ifthe cell provides good RSRP/RSRQ measurements without any powerboosting, thereby providing a mechanism for controlling traffic levels.

A simpler version of a PBA whitelist might simply indicate cell IDs thatare able to provide PBA at a pre-defined (e.g. specified or agreed)level. This approach is broadly equivalent to the ‘single level’indication approach described above.

It will be appreciated that a conventional LTE network allows for thedefinition of so-called white-lists and black lists of PCIs. A whitelist is a list of PCIs for which a terminal device is required to makereference signal measurements, and other cells may also be measured. Ablack list instructs a terminal device not to measure any black-listedPCIs for neighbour cell reselection. The configurations of these PCIwhite and black lists are sent via RRC (Radio Resource Control)signalling as part of the RRM (Radio Resource Management)configurations. The black list may be used to prevent a terminal devicefrom reselecting to specific intra- and inter-frequency neighbouringcells. This existing white and black this functionality can complementthe power boost availability white list concepts described herein.

The above-described embodiments have focused primarily on methods ofoperation in accordance with embodiments of the invention for a terminaldevice in an idle mode. However, corresponding principles may be appliedwhere a terminal device is in a connected mode, for example to assisthandover procedures.

When a terminal device is in RRC_CONNECTED mode, such that mobility isunder control of E-UTRAN, with assistance from terminal devicemeasurements, etc., a white-listing approach similar to that discussedabove may be adopted to in effect improve the relevance of the RRMmeasurements sent to the base station to ensure that handover decisionstake account of information regarding the extent to which different basestations support power boosting (and black lists can operate as normalalso). Similarly to in the RRC_IDLE case, this can help avoid terminaldevices making unnecessary reports for base stations/cells that theterminal device can detect, but which are not in its white-list andcannot support its coverage needs.

FIG. 9 is a ladder diagram schematically representing some operationalaspects of the terminal device 1403 and the base stations 1401A, B, C ofFIG. 6 for an example embodiment of the invention in which the terminaldevice is assumed to be in RRC connected mode with base station 1401A.

In a first step the terminal device wakes up after a quiescent period.In accordance with conventional LTE principles, the terminal devicescans for synchronisation signalling being broadcast by base stationswith a view to establishing whether it would be appropriate to handoverto another base station. As noted above, it is assumed for the examplearrangement of FIG. 6 the terminal device is within the nominal coveragearea of all three base stations 1401A, B, C. Thus, and as schematicallyrepresented in FIG. 9, the terminal device is able to receive primary(PSS) and secondary (SSS) signalling from each of the base stations. Inaccordance with the principles described above, the respective basestations which support power boosting are configured to indicate this bymaking transmissions in association with their synchronisationsignalling (e.g. signalling repetitions) on transmission resourcesspecifically defined for this purpose. This is schematically representedin FIG. 9 for the base stations which support power boosting (i.e. basestations 1401A and 1401B) by the labelling “PBA indicated” associatedwith the representation of their PSS/SSS signalling. A base stationwhich does not support power boosting (such as base station 1401C) doesnot make transmissions associated with synchronisation signalling on thepre-defined transmission resources, thereby in effect indicating itsinability to use power boosting (as represented in FIG. 9 by thelabelling “PBA not indicated” for the PSS/SSS signalling from basestation 1401C).

In a manner similar to the embodiments described above, the terminaldevice 1403 is configured to search for synchronisation signallingrepetitions on the transmission resources defined for indicating theavailability of power boosting, and if such synchronisation signallingis found, the terminal device 1403 determines the corresponding basestation supports power boosting. Thus the terminal device 1403determines that the base stations 1401A and 1401B support powerboosting, whereas the base station 1401C does not. Thus, the terminaldevice 1403 reaches a stage at which it has identified what basestations are in range and which of them support power boosting.

In the next two stages represented in FIG. 9 the terminal device 1403establishes which base station has the potential (taking account ofpower boosting availability) for providing the optimum channelconditions. This is based on RSRP measurements for each base station anda ranking process that takes account of the availability of powerboosting for the respective base stations. These stages may be performedin broadly the same manner as for the corresponding steps of FIG. 7.

In the example of FIG. 7 (cell selection from RRC idle) the terminaldevice determines from the cell ranking procedure which base station itwill proceed to camp on. However, in the example of FIG. 9 the terminaldevice is already connected to base station 1401A. Thus after the cellranking stage represented in FIG. 9, the terminal device proceeds withsending a measurement report to the base station 1401A regarding theRSRP measurements that have been made for the neighbouring cells. Ingeneral the procedures and format for sending this report may followestablished practices for LTE type networks. However, a significantdifference from conventional schemes in this example embodiment is thatthe measurement report sent from the terminal device 1403 to the basestation 1401A will based on RSRP measurements which have been modifiedto take account of the availability of power boosting (e.g. by adding anoffset based on the indicated over the power boosting) in accordancewith the principles described above.

When the base station 1401A to which the terminal device 1403 is campedon receives the measurement report, it may proceed as normal todetermine whether or not to handover the terminal device to another basestation. That is to say, from the point of view of the base station thehandover procedure may be conventional. That is to say, it does notmatter for the subsequent procedure that the handover decision is beingbased on modified (as opposed to actual) RSRP measurements received fromthe terminal device 1403.

In this example it is assumed the measurement report from the terminaldevice indicates that base station 1401B is associated with betteroperating conditions for the terminal device 1403, or at least it wouldbe when using the power boosting it can support. Accordingly, the basestation 1401A makes a decision to handover the terminal device to basestation 1401B as schematically represented in the next stage of FIG. 9.In accordance with established techniques, the base station 1401A(handover source cell), the base station 1401B (handover target cell),and the terminal device 1403 exchange signalling to allow the terminaldevice to switch to our syndicated mode with base station 1401B andreport when this is complete, as schematically represented in FIG. 9.

In a variation of the approach of FIG. 9, the respective base stationsmight not communicate an indication of the extent to which they supportpower boosting to the terminal device. The terminal device may thereforemake RSRP measurements and provide a measurement report in accordancewith conventional techniques. The base station to which the terminaldevice is RRC connected may then make a handover decision based on theconventional RSRP measurements reported by the terminal device inconjunction with information regarding the extent to which neighbouringbase stations support power boosting. That is to say, the base stationitself may be responsible for in effect modifying the RSRP measurementsreceived from the terminal device to take account of available powerboosting in neighbouring cells. For example, the base station may add anappropriate power offset to the RSRP measurements associated with theother base stations based on information received from other stations,for example over X2 signalling as discussed above, regarding theirability to support power boosting.

Although embodiments of the invention have been described with referenceto an LTE mobile radio network, it will be appreciated that the presentinvention can be applied to other forms of network such as GSM, 3G/UMTS,CDMA2000, etc. The term MTC terminal as used herein can be replaced withuser equipment (UE), mobile communications device, terminal device etc.Furthermore, although the term base station has been usedinterchangeably with eNodeB it should be understood that there is nodifference in functionality between these network entities.

Thus, a wireless telecommunication system is described which comprisesbase stations for communicating with terminal devices. One or more basestations support a power boost operating mode in which a base station'savailable transmission power is concentrated in a subset of itsavailable transmission resources to provide enhanced transmission powersas compared to transmission powers on these transmission resources whenthe base station is not operating in the power boost mode. A basestation establishes an extent to which one or more base stations in thewireless telecommunications system support the power boost operatingmode conveys an indication of this to a terminal device. The terminaldevice receives the indication and uses the corresponding information tocontrol its acquisition of a base station of the wirelesstelecommunication system, for example by taking account of which basestations support power boosting and/or when power boosting is supportedduring a cell attach procedure.

Embodiments of the invention can thus allow a network operator toprovide for additional information to be conveyed to terminal devices asregards the suitability of different cells for meeting the terminaldevices' needs. This can help to reduce wasted connection attempts bythe terminal device. This can in turn reduce power wastage at theterminal, and could reduce uplink interference on PRACH since in generalfewer terminal devices may attempt to acquire certain cells. Theconfigurable nature of approached in accordance with embodiments of theinvention means that an operator might enable coverage extension (powerboosting) only at selected times of the day, for example to provide abalance between cell efficiency and coverage, rather than having toalways tolerate some degree of sacrifice, and thus inefficient resourceand power use, for both. In RRC IDLE, a terminal device may be able toavoid choosing to camp on a cell which will not be able to support itwhen the terminal device eventually becomes RRC_CONNECTED. The terminaldevice is therefore able to avoid the power wastage of listening forpaging and SI on such cells. Such cells also need not be stored in thetypically limited space for the list of candidate cells for cellre-selection.

Embodiments of the invention can also allow a terminal device (UE) tosleep for relatively long periods of time, and to only wake up when thenetwork has indicated it will be able to serve it efficiently (becausepower boosting will be available), again offering the potential forsignificant reductions in power consumption. These consequences may beparticularly relevant in some MTC scenarios where a terminal device maybe in an inaccessible location and may have a limited battery life.

Embodiments of the present disclosure may be applied in a wirelesstelecommunications system supporting virtual carrier modes of operation.A virtual carrier represents a restricted subset of downlinktransmission resources within the overall transmission resource gridassociated with a host carrier which may be used for communicating atleast some information with certain types of terminal devices, forexample, reduced capability machine type communication terminal devices.Thus, virtual carrier operation may be summarised as an approach in awireless telecommunications system in which downlink communications aremade by a base station using a radio interface that spans a systemfrequency bandwidth and a terminal device is configured to receive atleast some communications from the base station within a restrictedsubset of transmission resources selected from within the systemfrequency bandwidth and comprising a restricted bandwidth downlinkchannel having a channel bandwidth which is smaller than the systemfrequency bandwidth.

A primary driver for some types of terminal device, for example MTCdevices, will be a desire for such devices to be relatively simple andinexpensive. For example, the type of functions typically performed byan MTC-type terminal (e.g. simple collection and reporting/reception ofrelatively small amounts of data) do not require particularly complexprocessing to perform, for example, compared to a smartphone supportingvideo streaming. However, third and fourth generation mobiletelecommunication networks typically employ advanced data modulationtechniques and support wide bandwidth usage on the radio interface whichcan require more complex and expensive radio transceivers and decodersto implement. It is usually justified to include such complex elementsin a smartphone as a smartphone will typically require a powerfulprocessor to perform typical smartphone type functions. However, asindicated above, there is now a desire to use relatively inexpensive andless complex devices which are nonetheless able to communicate usingLTE-type networks.

With this in mind there has been proposed a concept of so-called“virtual carriers” operating within the bandwidth of a “host carrier”,for example, as described in GB 2 487 906 [7], GB 2 487 908 [8], GB 2487 780 [9], GB 2 488 513 [10], GB 2 487 757 [11], GB 2 487 909 [12], GB2 487 907 [13] and GB 2 487 782 [14]. One principle underlying theconcept of a virtual carrier is that a frequency subregion (subset offrequency resources) within a wider bandwidth (greater range offrequency resources) host carrier is configured for use as aself-contained carrier for at least some types of communications withcertain types of terminal device. For example, a terminal device may beconfigured to receive at least some communications from the base stationwithin a restricted subset of transmission resources selected fromwithin the system frequency bandwidth whereby the restricted subset oftransmission resources comprises a downlink channel having a channelbandwidth which is smaller than the system frequency bandwidth.

In some virtual carrier implementations, such as described in references[7] to [14], all downlink control signalling and user-plane data forterminal devices using the virtual carrier may be conveyed within thesubset of frequency resources associated with the virtual carrier. Aterminal device operating on the virtual carrier is made aware of therestricted frequency resources and need only receive and decode acorresponding subset of transmission resources to receive data from thebase station. One advantage of this approach is to provide a carrier foruse by low-capability terminal devices capable of operating over onlyrelatively narrow bandwidths. This allows devices to communicate onLTE-type networks, without requiring the devices to support fullbandwidth operation. By reducing the bandwidth of the signal that needsto be decoded, the front end processing requirements (e.g., FFT, channelestimation, subframe buffering etc.) of a device configured to operateon a virtual carrier are reduced since the complexity of these functionsis generally related to the bandwidth of the signal received.

Other virtual carrier approaches for reducing the required complexity ofdevices configured to communicate over LTE-type networks are proposed inGB 2 497 743 [15] and GB 2 497 742 [16]. These documents propose schemesfor communicating data between a base station and a reduced-capabilityterminal device whereby physical-layer control information for thereduced-capability terminal device is transmitted from the base stationusing subcarriers selected from across a full host carrier frequencyband (as for conventional LTE terminal devices). However, higher-layerdata for reduced-capability terminal devices (e.g. user-plane data) istransmitted using only subcarriers selected from within a restrictedsubset of carriers which is smaller than and within the set ofsubcarriers comprising the system frequency band. Thus, this is anapproach in which user-plane data for a particular terminal device maybe restricted to a subset of frequency resources (i.e. a virtual carriersupported within the transmission resources of a host carrier), whereascontrol signalling is communicated using the full bandwidth of the hostcarrier. The terminal device is made aware of the restricted frequencyresource, and as such need only buffer and process data within thisfrequency resource during periods when higher-layer data is beingtransmitted. The terminal device buffers and processes the full systemfrequency band during periods when physical-layer control information isbeing transmitted. Thus, the reduced-capability terminal device may beincorporated in a network in which physical-layer control information istransmitted over a wide frequency range, but only needs to havesufficient memory and processing capacity to process a smaller range offrequency resources for the higher-layer data. This approach maysometimes be referred to as a “T-shaped” allocation because the area ofthe downlink time-frequency resource grid to be used by thereduced-capability terminal device may in some cases comprise agenerally T-shape.

Virtual carrier concepts thus allow terminal devices having reducedcapabilities, for example in terms of their transceiver bandwidth and/orprocessing power, to be supported within LTE-type networks.

In some wireless telecommunications systems it can be expected thatterminal devices reliant on power boosting modes of operation may alsorely on virtual carrier modes of operation. It may also be expected thatin some wireless telecommunications systems, some base stations maysupport virtual carrier operating modes, whereas some a stations may notsupport virtual carrier operating modes. Therefore, in some exampleembodiments of the present disclosure it can also be helpful for aterminal device to be made aware of whether or not base stations towhich it might seek to connect/attach support virtual carrier mode ofoperation. This is to help avoid a terminal device that relies onvirtual carrier operation seeking to attach to a base station that doesnot support a virtual carrier mode of operation. In many respects thisissue mirrors the issues described above for helping to avoid a terminaldevice that relies on power boost operation seeking to attach to a basestation that does not support a power boost mode of operation. In thisregard, it will be appreciated many of the comments provided above inthe context of power boosting operations apply equally in the context ofvirtual carrier operations.

Thus certain embodiments of the invention may be directed to schemes forproviding terminal devices with information on base stations'capabilities to operate in a virtual carrier mode (e.g. in terms ofif/when a base station supports virtual carrier operation) with a viewto reducing wasted camp on attempts. A terminal device may thus controlits acquisition of a base station of a wireless telecommunicationssystem based on information received from one or more base stationsregarding the extent to which one or more base stations in the wirelesstelecommunications system support a virtual carrier mode of operation.By taking account of different base stations' capabilities with regardto the virtual carrier mode of operation a terminal device may be ableto more efficiently control its acquisition of a base station inaccordance with embodiments of the disclosure. For example, if aterminal device relies on virtual carrier operation it might avoidattempting to attach to base stations which do not support virtualcarrier operation and/or might delay accessing a base station until alater time when virtual carrier operation is available for the basestation.

As described above, in accordance with certain embodiments of thepresent disclosure, a base station may be configured to provide aterminal device with information regarding the extent to whichneighbouring base stations support power boosting. Similarly, inaccordance with certain other embodiments, a base station may, inaddition or in the alternative, be configured to provide a terminaldevice with information regarding the extent to which one or moreneighbouring base stations support virtual carrier operations.

As noted above, when an idle mode terminal device is already camped onan initial cell/base station, it may be appropriate to consider movingto another cell, for example because the quality of signallingassociated with the initial cell has deteriorated and/or the device haschanged location (i.e. due to mobility). A terminal device may inaccordance with embodiments of the present disclosure perform a cellreselection procedure taking account of the extent to which differentbase stations offer virtual carrier operation. For cell reselection theterminal device has already camped on to a base station of the networkand so will have had access to system information. Thus in accordancewith some embodiments of the invention, information conveyed in systeminformation may be used to provide an indication of the extent to whichdifferent base stations support virtual carrier operation in the networkto assist terminal devices control their acquisition of base stations.This type of approach may be provided in conjunction with the signallingapproaches for conveying information regarding the abilities of basestations to support power boosting such as described above (whetherimplicit or through system information), or may be providedindependently of this. That is to say, the approaches described hereinfor conveying power boost indications (i.e. indications of the extent towhich base stations support power boost modes of operations) may equallybe adopted for conveying virtual carrier indications (i.e. indicationsof the extent to which base stations support virtual carrier modes ofoperations), and this may be done in conjunction with, or separately andindependent from, any conveying of power boost indications. Indeed,approaches for conveying indications of the extent to which one or morebase stations support virtual carrier modes of operations as describedherein may be implemented in a wireless telecommunication system thatdoes not support power boost operations, and vice versa.

Thus, in accordance with some embodiments the concept of a list of whichbase stations support virtual carrier operation within a wirelesstelecommunications system, and potentially characteristics of thevirtual carrier operation they offer, for example in terms of frequencyresources used for virtual carrier operation, times during which virtualcarrier operation is available, and so forth, may be introduced. Thismay conveniently be referred to as a white list for virtual carrieravailability. The list may, for example, be broadcast by the basestation in association with system information normally received byterminal devices attached to the base station. Thus, terminal deviceswhich are already connected to a station may be readily provided withinformation regarding the extent to which other base stations in thenetwork support virtual carrier operation. This information can assistterminal devices determine whether to move to another base station byallowing terminal devices to take account of whether the other basestation can support the terminal device in a virtual carrier operatingmode. The following table represents an example virtual carrieravailability white list linking communication cell identities (PCIs) toan indication of whether or not the respective cells support virtualcarrier operations.

Virtual carrier Cell ID operation? 43 Yes 432 No 124 No 156 YesEach base station may be configured to maintain the white list forcommunication to their connected terminal devices. The list may bemaintained (semi)dynamically based on communications between basestations regarding their support for a virtual carrier operation, forexample using the X2 interface between base stations using newly-definedextra information elements. For an example, individual base stations maycommunicate to neighbouring base stations using X2 signalling shouldthey change their support for a virtual carrier operation.Alternatively, the list may be (semi)static based on an operatorselected network configuration. Thus, when a terminal device in idlemode measures the RSRP/RSRQ of Cell ID 432 it may determine the cell isassociated with good channel conditions, but should nonetheless beavoided because it does not (currently) support virtual carrieroperations.

Thus, in accordance with some embodiments, a serving cell to which aterminal device has already connected may provide a VC (virtual carrier)indication relevant for a neighbouring cell or cells. If a terminaldevice is connected to the serving cell (possibly, but not necessarily,after deciding to connect in a manner taking account of indications ofpower boost availability such as described above), RRC configurationsignalling can be used to convey VC indications relevant for other basestation(s)/cell(s).

As noted above in the context of conveying neighbour cell power boostinginformation, neighbour cell VC information can also be provided to idleterminal devices by including relevant information in the SystemInformation (SI) broadcasts. Idle-mode terminal devices checkperiodically for SI changes by checking a configured pattern ofsubframes for a paging PDCCH which identifies the PDSCH resources inwhich the SI is held in the subframe. This provides a mechanism for idlemode terminal devices to receive explicit signalling regarding one ormore base stations' capabilities as regards virtual carrier operations.

A simpler version of a VC whitelist might simply indicate cell IDs thatare able to support virtual carrier operations (or conversely, whichcell IDs are unable to support virtual carrier operations).

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. It will beappreciated that features of the dependent claims may be combined withfeatures of the independent claims in combinations other than thoseexplicitly set out in the claims.

REFERENCES

-   -   [1] Holma, H. and Toskala, A., “LTE for UMTS OFDMA and SC-FDMA        based radio access”, John Wiley and Sons, 2009    -   [2] GB 1305233.7—filed 21 Mar. 2013    -   [3] GB 1305234.5—filed 21 Mar. 2013    -   [4] ETSI TS 136 304 V11.2.0 (2013-02)/3GPP TS 36.304 Version        11.2.0 Release 11    -   [5] ETSI TS 123 122 V11.4.0 (2013-01)/3GPP TS 23.122 Version        11.4.0 Release 11    -   [6] ETSI TS 136 101 V11.3.0 (2013-02)/3GPP TS 36.101 Version        11.3.0 Release 11    -   [7] GB 2 487 906 (UK patent application GB 1101970.0)    -   [8] GB 2 487 908 (UK patent application GB 1101981.7)    -   [9] GB 2 487 780 (UK patent application GB 1101966.8)    -   [10] GB 2 488 513 (UK patent application GB 1101983.3)    -   [11] GB 2 487 757 (UK patent application GB 1101853.8)    -   [12] GB 2 487 909 (UK patent application GB 1101982.5)    -   [13] GB 2 487 907 (UK patent application GB 1101980.9)    -   [14] GB 2 487 782 (UK patent application GB 1101972.6)    -   [15] GB 2 497 743 (UK patent application GB 1121767.6)    -   [16] GB 2 497 742 (UK patent application GB 1121766.8)

1. A terminal device for use in a wireless telecommunication systemcomprising one or more base stations which support a virtual carrieroperating mode in which at least some downlink communications are madeusing a restricted subset of transmission resources selected from withina system frequency bandwidth and comprising a restricted bandwidthdownlink channel having a channel bandwidth which is smaller than thesystem frequency bandwidth, wherein the terminal device is configured toreceive an indication of the extent to which one or more base stationssupport the virtual carrier operating mode in the wirelesstelecommunication system; and to control acquisition of a base stationof the wireless telecommunication system in a manner that takes accountof the indicated extent to which one or more base stations support thevirtual carrier operating mode.
 2. The terminal device of claim 1,configured to receive the indication of the extent to which one or morebase stations support the virtual carrier operating mode by receivingfrom a first base station an indication of the extent to which a second,different, base station supports the virtual carrier operating mode. 3.The terminal device of claim 1, configured such that the first basestation is a base station to which the terminal device is connected andthe second base station is a base station to which the terminal deviceis not connected.
 4. The terminal device of claim 1, configured suchthat the indication of the extent to which one or more base stationssupport the virtual carrier operating mode is received by the terminaldevice using explicit signalling.
 5. The terminal device of claim 4,wherein the explicit signalling comprises system information signallingreceived from a base station.
 6. A terminal device for use in a wirelesstelecommunication system comprising one or more base stations whichsupport a power boost operating mode in which a base station's availabletransmission power is concentrated to provide enhanced transmissionpowers in a subset of its available transmission resources, wherein theterminal device is configured to: receive an indication of the extent towhich one or more base stations support the power boost operating modein the wireless telecommunication system; and control acquisition of abase station of the wireless telecommunication system in a manner thattakes account of the indicated extent to which one or more base stationssupport the power boost mode.
 7. The terminal device of claim 6, whereinthe terminal device is configured to receive the indication of theextent to which one or more base stations support the power boostoperating mode by receiving from a first base station an indication ofthe extent to which the first base station supports the power boostoperating mode.
 8. The terminal device of claim 7, wherein the terminaldevice is configured to receive the indication of the extent to whichone or more base stations support the power boost operating mode byreceiving from a further base station an indication of the extent towhich the further base station supports the power boost operating mode.9. The terminal device of claim 6, wherein the terminal device isconfigured to receive the indication of the extent to which one or morebase stations support the power boost operating mode by receiving from afirst base station an indication of the extent to which a second,different, base station supports the power boost operating mode.
 10. Theterminal device of claim 9, wherein the first base station is a basestation to which the terminal device is connected and the second basestation is a base station to which the terminal device is not connected.11. The terminal device of claim 10, wherein the terminal device isconfigured to control acquisition of a base station of the wirelesstelecommunication system by determining whether or not to disconnectfrom the first base station and to connect to the second base station.12. The terminal device of claim 6, wherein the terminal device isconfigured to receive the indication of the extent to which one or morebase stations support the power boost operating mode in communicationsreceived from one or more base station to which terminal device is notconnected.